Involuntary movements have often been difficult to classify clinically. Clinical and physiological analysis of a continuing series of patients has led to new classifications and pathophysiological insights. Patients with myoclonus have been studied to seek further understanding of this confusing involuntary movement. Extensive studies have classified most cases seen within previously identified categories. We are trying to define criteria that would delineate hysterical myoclonus unambiguously. We have studied some patients with periodic movements in sleep and dyskinesias while awake in patients with the restless legs syndrome. We have seen that some of these involuntary movements share a similar appearance to normal flexor reflexes. Detailed clinical and physiologic studies have been done in patients with palatal tremor (myoclonus). We have further data confirming the division of these patients into two groups: idiopathic and secondary. We have studied three patients with stiff-man syndrome seeking to understand the pathophysiology. We have found abnormalities in presynaptic inhibition in all. Other abnormalities are not consistent. Other investigations include a study of movement related cortical potentials in patients with tic and a physiologic investigation of facial twitching seen in patients with olivopontocerebellar atrophy. A therapeutic trial with trazadone is in progress for patients with essential tremor that has not responded to standard therapy. Preliminary results show that some patients will benefit from this drug. We have studied several patients in a family with hyperekplexia. Our results showed that movement in these patients is an exaggerated startle reflex.